The long-range goal of the research is to ascertain the way in which early interactions between epithelial and mesenchymal tissues determine the different cellular phenotypes in the rat salivary glands. One line of research will use biochemical, immunochemical and imunocytochemical methods to further define and characterize secretory proteins that have a unique distribution in each different cell type of the major salivary glands and perhaps related glands, and use these as sensitive indicators of cellular phenotype. These studies will test the hypothesis that at least one secretory protein (SMG-A) is a characteristic gene product of both the neonatal submanibular and parotid glands, and later disappears from the submandibular and is maintained in the parotid as a major adult secretory product. They also will determine whether the neonatal Type III cells of the submandibular gland transform directly into adult mucous cells. Secondly, the unique but related pattern of proteins in each salivary cell type will be used to define the type of cellular differentiation that will occur in organ cultures and in novel epithelial and mesenchymal recombinations of salivary rudiments. Lastly, we shall determine whether intercalated ducts of the adult submandibular gland retain the potential to recapitulate the embryonic developmental program. We anticipate that the results will permit the formulation of useful hypotheses concerning both the organization and regulation of the genes for the salivary proteins, and the biochemical basis for the mesencymal specification of cellular phenotypes.